The present invention relates to a developing apparatus, an image forming apparatus, an image forming system, and an image forming method.
An image forming apparatus such as a laser beam printer is known well. Such an image forming apparatus includes an image carrier holding a latent image and a developing apparatus developing the latent image held by the image carrier by the use of a developer. When an image signal, etc. is transmitted from an external apparatus such as a computer, the image forming apparatus forms a developer image and then transfers the developer image onto a medium, thereby finally forming an image on the medium.
The developing apparatus includes a developer carrier rotating with a developer held thereon and the developer carrier develops the latent image held by the image carrier by the use of the developer. Concave portions regularly arranged might be formed on the surface of the developer carrier so as to hold a sufficient amount of developer. The developing apparatus might be provided with a contact member being made of a rubber elastic body and coming in contact with the surface of the developer carrier. An example of the contact member is a layer thickness regulating member regulating the layer thickness of the developer held by the developer carrier.
Patent Document 1: Japanese Patent Publication No. 2006-259384A
It is known that the contact member made of a rubber elastic body exhibits a rubber-like characteristic or a glass-like characteristic depending on the temperature of the contact member. At the temperature at which the contact member usually operates, the contact member exhibits the rubber-like characteristic. Accordingly, even when the contact member is disposed in the developing apparatus, it is required that the contact member should be used with the rubber-like characteristic.
It is also known that the contact member may vibrate and the contact member exhibits the rubber-like characteristic or the glass-like characteristic depending on the magnitude of the vibration frequency. That is, it is assumed that a value obtained by dividing the loss elastic modulus of the contact member by the storage elastic modulus is a loss tangent (tan δ). Then, when the frequency of the contact member is greater than the frequency at which the loss tangent (tan δ) is the greatest (hereinafter, also referred to as “greatest loss tangent frequency”), the contact member exhibits the glass-like characteristic. On the other hand, when the frequency of the contact member is smaller than the greatest loss tangent frequency, the contact member exhibits the rubber-like characteristic.
As described above, the contact member is in contact with the surface (which includes the concave portions) of the developer carrier and the developer carrier frictionally slides on the contact member at the time of rotation thereof, thereby causing the contact member to vibrate. When the number of vibrations of the contact member vibrating with the rotation of the developer carrier is greater than the greatest loss tangent frequency, the contact member exhibits the glass-like characteristic and thus the above-mentioned requirement cannot be satisfied.
It is known that the contact member may vibrate with the rotation of the developer carrier and the contact member exhibits the rubber-like characteristic or the glass-like characteristic depending on the number of vibrations. Accordingly, in order to satisfy the above-mentioned requirement, it is preferable that the frequency of the contact member at the time of the rotation of the developer carrier is controlled so as for the contact member to exhibit the rubber-like characteristic.
On the other hand, when the contact member is used with the rubber-like characteristic, abnormal noises may be generated with the vibration of the contact member. Here, the contact member made of the rubber elastic body exhibits dynamic viscoelasticity (an elastic behavior and a viscous behavior). When the elastic behavior of the two behaviors is superior, the amplitude of the vibration of the contact member increases and thus the abnormal noises are easily generated.
It is known that the contact member may vibrate with the rotation of the developer carrier and the contact member exhibits the rubber-like characteristic or the glass-like characteristic depending on the magnitude of the number of vibrations. Accordingly, in order to satisfy the above-mentioned requirements it is preferable that the frequency of the contact member is controlled so as for the contact member to exhibit the rubber-like characteristic.
On the other hand, when the contact member is used with the rubber-like characteristic, the temperature of the contact member may rise with the vibration of the contact member. Here, the contact member made of the rubber elastic body exhibits dynamic viscoelasticity (an elastic behavior and a viscous behavior). When the viscous behavior of the two behaviors is superior, the molecular chains constituting the contact member easily vibrates and thus heat may be easily generated. As a result, the temperature of the contact member easily rises.
As described above, the contact member is in contact with the surface of the developer carrier and the surface of the developer carrier is provided with concave portions regularly arranged. Accordingly, when the developer carrier rotates, the developer carrier slides on the contact member and thus the contact vibrates.
When the number of vibrations of the contact member (the value obtained by dividing the movement speed of the surface with the rotation of the developer carrier by the pitch of the concave portions in the peripheral direction of the developer carrier corresponds to the number of vibrations) is too great, it is known that the contact member made of the rubber elastic body exhibits the glass-like characteristic, not the rubber-like characteristic. Accordingly, at the time of development, it is necessary to allow the developer carrier to rotate at a rotation speed at which the frequency is too great (that is, the contact member does not exhibit the glass-like characteristic).
However, when the development is made in a state where the contact member exhibits the rubber-like characteristic, a filming is generated in the contact member due to tackiness of the contact member based on the rubber-like characteristic. When the filming becomes remarkable, the quality of an image developed and finally formed on the medium is deteriorated.